8 replies to this topic

[Gaz66]

Just throwing this out there to see what the general opinions are.
Is there really any need to drill and tap the block to 5/16 unf for the gearbox to block bolts on a competition engine?
Anyone had any trouble with the 1/4 unf bolts?

Edited by Gaz66, 28 January 2025 - 05:16 PM.

[imack]

I've always drilled and tapped for 5/16" unf bots. Whether it makes any difference, I've no idea.
5/16 bolts are a faff to get a spanner or allen key onto.

Edited by imack, 28 January 2025 - 05:20 PM.

[Spider]

I've never found the need to go bigger than the original 1/4"UNF Screws.

[GraemeC]

I've always drilled and tapped for 5/16" unf bots. Whether it makes any difference, I've no idea.
5/16 bolts are a faff to get a spanner or allen key onto.

Long, ball end hex driver with a 3/8” or 1/4” square drive for a ratchet or T handle works well for all but the two over the diff.

[nicklouse]

Did it as I had the time and the kit.

 

keeping original and using Allen head sockets could make life easier.

 

i can think of better things like a hole in the subframe so you can get all the Wok bolts.

[Cooperman]

I have never used anything other than the original 1/4" bolts even on 100+ bhp competition engines.

There has never been any issue with the 1/4" bolts, so why try to fix a problem which doesn't exist.

Edited by Cooperman, 28 January 2025 - 09:29 PM.

[Gaz66]

Thinking about this a bit more it probably came about after some 1/4 unf threads were stripped and they needed to be tapped the next size up in order to still use the block.
Probably then sold as a competition "mod" after that.

[DeadSquare]

The only force separating the block from the gearbox comes from the transfer gears, and the transfer case straps them together, so why weaken the aluminium casing by enlarging the holes ?

[Gaz66]

I found the very same question being asked in 2011 after a search on here.
It seems people including Vizard were having trouble blowing gaskets and snapping 1/4" bolts.
Apparently Vizard did this mod on all long stroke engines as they were the problem along with thin flanged blocks.